U.S. patent application number 11/308167 was filed with the patent office on 2007-09-13 for method and device including reworkable alpha particle barrier and corrosion barrier.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Rehan Choudhary, Benjamin V. Fasano, Sushumna Iruvanti, Daniel D. Reinhardt, Deborah A. Sylvester.
Application Number | 20070212820 11/308167 |
Document ID | / |
Family ID | 38479451 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070212820 |
Kind Code |
A1 |
Choudhary; Rehan ; et
al. |
September 13, 2007 |
METHOD AND DEVICE INCLUDING REWORKABLE ALPHA PARTICLE BARRIER AND
CORROSION BARRIER
Abstract
A method and device comprising an easily reworkable alpha
particle barrier is provided. The easily reworkable alpha particle
barrier is applied in the space between the surface of the chip and
the surface of the substrate, and reduces soft error rate (SER).
Further, the easily reworkable alpha particle barrier material is
chosen from the group of an organic material, a hydrocarbon, more
specifically a polyalphaolefin (PAO) oil, and a polymer or filled
polymer; wherein the polyalphaolefin oil has a viscosity below 1000
cSt (at 100.degree. C.). The easily reworkable alpha particle
barrier material can be used with multichip modules (MCM's)
allowing easy device rework of one or more dies without affecting
other dies on the same substrate.
Inventors: |
Choudhary; Rehan;
(Poughkeepsie, NY) ; Fasano; Benjamin V.; (New
Windsor, NY) ; Iruvanti; Sushumna; (Wappingers Falls,
NY) ; Reinhardt; Daniel D.; (Hinesburg, VT) ;
Sylvester; Deborah A.; (Poughkeepsie, NY) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
International Business Machines
Corporation
New Orchard Road
Armonk
NY
10504
|
Family ID: |
38479451 |
Appl. No.: |
11/308167 |
Filed: |
March 9, 2006 |
Current U.S.
Class: |
438/118 |
Current CPC
Class: |
H01L 2924/14 20130101;
H01L 2224/16225 20130101; H01L 2224/73204 20130101; H01L 24/32
20130101; H01L 2924/00014 20130101; H01L 2224/05573 20130101; H01L
2224/73203 20130101; H01L 21/563 20130101; H01L 2224/8388 20130101;
H01L 24/13 20130101; H01L 2224/73204 20130101; H01L 2224/83885
20130101; H01L 2924/00014 20130101; C08L 71/00 20130101; H01L 24/16
20130101; H01L 2224/05568 20130101; C08G 2650/40 20130101; H01L
2924/3512 20130101; H01L 24/29 20130101; H01L 2924/12044 20130101;
H01L 23/556 20130101; H01L 2224/32225 20130101; H01L 2924/01084
20130101; H01L 2924/00 20130101; H01L 2224/32225 20130101; H01L
2924/12044 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2224/05599 20130101; H01L 2224/16225 20130101 |
Class at
Publication: |
438/118 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Claims
1. A method of protecting electronic circuits comprising: providing
at least one integrated circuit (IC) chip electrically connected to
a corresponding pad on a substrate; and providing an easily
reworkable alpha blocking material in a gap between the IC chip and
the substrate on at least one side of the gap, an IC chip side or a
substrate side.
2. The method of claim 1, wherein the easily reworkable alpha
blocking material is selected from one or more of a hydrocarbon
oil, and a thermoplastic polymer.
3. The method of claim 1 wherein the easily reworkable alpha
blocking material comprises a suspension and/or a mixture of oil
and inorganic filler, or a filled-polymer.
4. The method of claim 1, wherein the easily reworkable alpha
blocking material further includes a viscosity-lowering solvent
selected from at least one of paraffins, alcohols, ethers, esters,
amides, lactones, ketones, sulfones, aromatic hydrocarbons,
N-methyl-pyrrolidone (NMP), diglyme, triglyme, xylene, amyl
acetate, and acetophenone.
5. The method of claim 1, wherein the easily reworkable alpha
blocking material is easily removed by washing with a cleaning
solvent and optionally dried with nitrogen.
6. The method of claim 1, wherein the easily reworkable alpha
blocking material is drawn into a gap between the surface of the IC
chip and a facing surface of the substrate by one or more of
capillary action, heating, and vibration, and wherein the easily
reworkable alpha blocking material is at least substantially
contained in the gap between a surface of the IC chip and a facing
surface of the substrate by at least one of o-rings, meshes, and
surface tension.
7. The method of claim 2, wherein the hydrocarbon oil comprises a
polyalpha olefin.
8. The method of claim 2, wherein the hydrocarbon oil has a
viscosity below 1000 cSt at 100.degree. C.
9. The method of claim 2, wherein the thermoplastic polymer
comprises a polymer selected from at least one of polyisobutylene,
polystyrene, acrylates, poly ethyl ether ketones, polyetherimide,
polyamides, and engineered thermoplastics, wherein the polymer has
a glass transition temperature (T.sub.g) between about -65.degree.
C. and 230.degree. C.
10. The method of claim 3, wherein the filled-polymer, suspension
and/or mixture comprises a metal powder filler selected from at
least one of carbon, Al.sub.2O.sub.3, SiO.sub.2, SnO.sub.2, BN,
AlN, SiC diamond, aluminum, nickel, copper, indium, boron, tin, and
silver, wherein said metal filler can optionally be coated with an
organic layer, polymides, barium titanate, Al.sub.2O.sub.3 or
SiO.sub.2.
11. A method for making an easily reworkable integrated circuit
chip electronic device comprising: providing a flip chip assembly
comprising at least one chip electrically connected to
corresponding pad on a substrate by a plurality of connections
between the at least one chip and the substrate, there being a gap
between the surface of the flip chip and the surface of the
substrate; and partially or fully filling the gap with an easily
reworkable alpha blocking material selected from one or more of an
organic material, a hydrocarbon oil or an oil-filler
mixture/suspension and a polymer or filled-polymer by dispensing
the material on at least one side of the gap between the chip and
the substrate.
12. The method of claim 11, wherein the easily reworkable alpha
blocking material has a viscosity below 1000 cSt at 100.degree.
C.
13. The method of claim 11, wherein the easily reworkable alpha
blocking material is at least substantially contained in a opening
between the surface of the chip and the surface of the substrate by
o-rings or meshes.
14. The method of claim 11, wherein the easily reworkable alpha
blocking material is drawn into the gap between the surface of the
chip and the surface of the substrate by a method selected from at
least one of capillary action, heating, and vibration; and wherein
the easily reworkable material remains in the opening between the
surface of the chip and the surface of the substrate by surface
tension.
15. The method of claim 11, wherein the polymer or filled-polymer
comprises at least one polymer selected from the group consisting
of poly ethyl ether ketones, polyetherimide, and engineered
thermoplastics, wherein the polymer or filled-polymer has a glass
transition temperature (T.sub.g) between about -65.degree. C. and
230.degree. C.
16. The method of claim 11, wherein the filled-polymer or
mixture/suspension comprises a metal powder filler selected from at
least one of carbon, Al.sub.2O.sub.3, SiO.sub.2, SnO.sub.2, BN,
AlN, SiC, diamond, aluminum, nickel, copper, indium, boron, tin,
and silver wherein said filler can optionally be coated with
polymides, barium titanate, Al.sub.2O.sub.3 or SiO.sub.2.
17. The method of claim 11, wherein the easily reworkable alpha
blocking material further includes a viscosity lowering solvent
selected from at least one of paraffins, alcohols, ethers, esters,
amides, lactones, ketones, sulfones, aromatic hydrocarbons,
N-methyl-pyrrolidone (NMP), diglyme, triglyme, xylene, amyl
acetate, and acetophenone.
18. A flip chip device which comprises an alpha particle barrier
material selected from an organic material, a PAO oil, a polymer,
and a filled-polymer; and wherein the alpha particle barrier
material is easily reworkable and has a viscosity less than 1000
cSt at 100.degree. C.
19. The flip chip device of claim 18, wherein the polymer or
filled-polymer comprises a polymer selected from at least one of
poly ethyl ether ketones, polyetherimide, and engineered
thermoplastics, wherein the polymer or filled-polymer has a glass
transition temperature (T.sub.g) between about -65.degree. C. and
230.degree. C.
20. The flip chip device of claim 18, wherein the filled-polymer
comprises a metal powder filler selected from at least one of
carbon, SiO.sub.2, SnO.sub.2, BN, AlN, SiC, diamond, aluminum,
nickel, copper, indium, boron, and tin, wherein said filler can
optionally be coated with polymides, barium titanate,
Al.sub.2O.sub.3 or SiO.sub.2.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to an easily reworkable
alpha particle barrier and C4 corrosion barrier. In some aspects
the invention also relates to a method of minimizing soft error
rate (SER) of electronic devices while allowing simple chip
rework.
BACKGROUND OF THE INVENTION
[0002] Electronic components utilizing integrated circuit chips are
used in a number of applications. Controlled Collapse Chip
Connection (C4 or "flip chip") is an interconnect technology
developed by IBM that provides a large chip to package I/O
capability. Typically, one or more integrated circuit chips are
mounted above a single or multiple layer substrate and pads on the
chip are electrically connected to corresponding pads on the
substrate by a plurality of electrical connections such as solder
bumps.
[0003] The die-attached flip chip package typically includes a gap
or space between the integrated circuit chip and the substrate
resulting from the overall height of the solder bump connection
between the chip and the substrate or adjacent carrier. The
substrate material and/or the interconnect solder can emit alpha
particles. Alpha particle emissions result from the radioactive
decay of impurity elements such as polonium, thorium and uranium in
the substrate or the interconnect solder. The alpha particles can
cause changes in both logic and memory functions of the device in
close proximity to the alpha particle source. Such a disruption of
the normal operation of the semiconductor devices is commonly
referred to as a soft error upset (SEU) and the overall
contribution to the performance of the device is described as the
soft error rate (SER).
[0004] The C4 joints are susceptible to cyclic fatigue cracking due
to the expansion mis-match between the chip and the underlying
substrate, or carrier. In order to improve the reliability of the
solder joints under cyclic field operating conditions of the
package (on/off), the gap is often filled with an underfill
material. The underfill material is often a particle-filled epoxy
compound that enhances the fatigue life of the C4. The underfill
material also helps to absorb the alpha particle radiation. The
fillers in the epoxy underfills should be of high purity to assure
that the underfill itself is not a source of alpha particles.
[0005] There are, however, packages that do not contain the
traditional epoxy underfill and hence are susceptible to SER. These
packages are typically large multi chip modules (MCMs) that require
chip reworkabilty for upgrades or defective chip replacement.
Removing the hardened, or cured underfill (such as the conventional
epoxy underfills) for chip rework is complicated, if not
impractical. There are also other packages which do not contain the
epoxy underfill such as those that do not suffer from the expansion
mis-match between the chip and the carrier, or those that are not
subjected to large cyclic temperature excursions in field
operation.
[0006] Earlier MCM packages contained thin film technology, a thin
film of metal and/or a polymer such as a polyimide on the
substrate, which provided the unintended benefit of absorbing the
alpha radiation from the substrate. However, thin film technology
tends to be very expensive. As described earlier, the use of
hardened, or cured epoxy underfill makes device rework extremely
difficult and economically unfeasible. Therefore, there is a need
to provide an effective alpha particle barrier that is easily
reworkable and cost efficient, and which minimizes or eliminates
SER.
SUMMARY OF THE INVENTION
[0007] In a first aspect, the invention provides a method of
protecting electronic circuits. The method comprises providing at
least one integrated circuit (IC) chip electrically connected to a
corresponding pad on a substrate. The method further includes
providing an easily reworkable alpha blocking material in a gap
between the IC chip and the substrate on at least one side of the
gap, an IC chip side or a substrate side.
[0008] In a second aspect, the invention provides a method for
making an easily reworkable integrated circuit chip electronic
device comprising providing a flip chip assembly comprising at
least one chip electrically connected to corresponding pads on a
substrate by a plurality of connections between the at least one
chip and the substrate. There is a gap between the surface of the
flip chip and the surface of the substrate. The method further
includes partially or fully filling the gap with an easily
reworkable alpha blocking material selected from one or more of an
organic material, a hydrocarbon oil or an oil-filler
mixture/suspension, and a polymer or filled polymer by dispensing
the material on at least one side of the gap between the chip and
the substrate.
[0009] A third aspect of the invention is a flip chip device which
comprises an alpha particle barrier material selected from the
group of an organic material, a PAO oil, a polymer, and a filled
polymer. The alpha particle barrier material is easily reworkable
and has a viscosity less than 1000 cSt at 100.degree. C.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIGS. 1-2 depict a device in accordance with the
invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0011] The invention relates to a method and/or device comprising
an easily reworkable alpha particle barrier layer which can also
act as a C4 corrosion barrier. More particularly, the invention
provides a device and method which includes an effective alpha
particle barrier layer that is easily reworkable and which
minimizes or eliminates SER. The invention is particularly
advantageous when used with multichip modules (MCM's) as it allows
easy device rework of one or more dies without affecting other dies
on the same substrate. The alpha particle barrier of the invention
additionally acts as a corrosion barrier, effectively keeping
moisture away from the package interconnect components.
[0012] Referring to FIG. 1, a cross-section is shown of an
electronic component 10 comprising an integrated circuit chip 11
and an interconnecting substrate 15. Integrated circuit chip 11 is
shown having conductive pads 12 electrically connected to
conductive pads 14 by solder connections 13 such as solder bumps,
in a method known as C4 or flip chip packaging. The lower surface
of substrate 15 may contain connectors (not shown), for connection
of the substrate 15 to another electronic device such as a circuit
board.
[0013] Electronic component 10 is shown in FIG. 1 as having an
easily reworkable alpha particle barrier layer 16 between pad
containing surface 17 of integrated circuit chip 11 and pad
containing surface 18 of substrate 15. The peripheral solder
connections 13 and pads 12 and 14 are shown as encapsulated by the
easily reworkable alpha particle barrier layer 16. In FIG. 2, the
easily reworkable alpha particle barrier layer 16 is shown as
completely encapsulating all of the solder connections 13.
[0014] Integrated circuit chip 11 may be any of a number of
integrated circuit devices such as a passive device or a very large
scale integration (VLSI) or ultra large scale integration (ULSI)
active device. Further, there may be at least one integrated
circuit chip present on substrate 15.
[0015] In a first embodiment, the reworkable alpha particle barrier
material comprises a low molecular weight oligomer/polymer, such as
a high viscosity grade hydrocarbon oil, for example,
polyalphaolefin (PAO) oil.
[0016] Examples of oils suitable as an easily reworkable alpha
particle barrier material in the first embodiment of the invention
may include high viscosity grade oils, such as PAO 100 cSt (Mobil
SHF 1003), 150, 300 or 1000 cSt (Spectrasyn.RTM. grades from Exxon
Mobil). The viscosity values correspond to those measured at
100.degree. C. These oils are not expected to interfere with
thermal interface materials (TIM) such as thermal paste, gels,
pads, solder, etc. if any, present on the substrate and/or chip.
Any oil, or low molecular weight oligomer/polymer is suitable for
the invention, provided that it performs the function of an alpha
particle barrier and can be easily removed with solvent cleaning or
other means (such as heating) for chip rework. Furthermore,
although oils are contemplated, any organic compound which acts as
an effective alpha particle barrier and which can be easily removed
with suitable solvent cleaning or other means can be used in the
present invention. Examples are gels, low molecular weight
thermoplastics, acrylates, coatings such as Parylene, etc.
[0017] Ideally, the material is selected so as to withstand chip
joining and operational temperatures, yet still allow device
reworking using conventional cleaning tools and methods. More
practically, the material is selected so as to withstand package
second-level attach to cards/boards, yet still allow chip rework
using conventional cleaning tools and methods. In oil embodiments,
the viscosity at 100.degree. C. is below 1000 cSt, preferably below
300 cSt, and in further embodiments below about 150 cSt.
[0018] Chip rework when using PAO oil or any suitable organic
compound as the reworkable alpha particle barrier, can be performed
for example, by washing with xylene, rinsing with a cleaning
solvent such as isopropanol (IPA), and then drying with nitrogen.
Additional suitable cleaning solvents include polar and non-polar
fluids, protic and aprotic fluids, including N-methylpyrolidone
(NMP), acetone, common aldehydes, ketones, tetrahydrofuran,
hexafluoroisopropanol (HFIP), and gamma-butyrolactone. However, any
conventional cleaning tool, solvent, or method can be used to
perform device reworking of the first embodiment of the present
invention.
[0019] It has been found that the first embodiment of the invention
is also capable of acting as a C4 corrosion barrier. For example,
use of neat PAO oil or a mixture of PAO oil and suitable
anti-oxidants such as Irganox.RTM. 1010 (antioxidant obtained from
Ciba Specialty Chemicals) individually or in combination with other
anti-oxidants can yield increased corrosion protection in
hermetically, semi-hermetically and non-hermetically sealed
packages. Although the exact mechanism is not fully understood, it
is believed that a hydrophobic layer coats the package components
such as the solder interconnect, keeping moisture away and thereby
minimizing or preventing corrosion in semi- and non-hermetic
environments. Oil-solid filler compositions such as slurries and
low-viscosity compounds (such as thermal paste/grease) can also be
used as an alpha particle barrier layer. These materials will
provide the additional benefit of better compatibility when used
with thermal paste/grease type TIMs.
[0020] In a second embodiment, the reworkable alpha particle
barrier layer comprises a polymer, or polymer/filler mixture or
suspension. Examples of polymers and compounds suitable as a
reworkable alpha particle barrier layers in the second embodiment
are low molecular weight thermoplastics, such as polysulfone,
polyisobutylene, acrylates, polystyrene, polyamides, etc. Other
polymers such as reworkable engineered thermoplastics (for example
Cookson Staystik.RTM. polymers available from Cookson Electronics),
poly ethyl ether ketones (for example OXPEKK.RTM. obtained from
Oxford Performance Materials, Inc.), and polyetherimide (for
example available as a polymer or filled polymer from GE Micronized
Polymers) may also be used. Suitable polymers will have a glass
transition temperature (T.sub.g) between about -65.degree. C. and
230.degree. C. and can be used neat or in combination with one
another.
[0021] Optionally, the polymers such as those noted above may be
filled with a ceramic or metal powder in a mixture or suspension.
Fillers are typically used to increase the thermal conductivity
and/or viscosity of the polymer and reduce the coefficient of
thermal expansion. Fillers can also function to block alpha
particle emissions from the package components and/or change the
dielectric properties of the alpha particle barrier material.
Examples of suitable fillers include metals such as aluminum,
nickel, copper, indium, boron, tin, and silver optionally with
insulating polymer or oxide coatings. Additionally, if a metal
powder is selected, it will ideally have electrically insulative
properties or be coated to be electrically non-conducting to reduce
C4-C4 shorting. Suitable coatings for the metal powder filler
include an organic layer, for example thermoplastic or thermoset
organics such as polyamides/polyimides, or oxides such as barium
titanate, Al.sub.2O.sub.3 or SiO.sub.2. Other examples of suitable
fillers include carbon, ceramic oxides such as Al.sub.2O.sub.3,
SiO.sub.2, SiC, SnO.sub.2, BN, AlN and diamond. The above noted
fillers can be used alone or in combination with each other.
Although any amount of filler is contemplated by the present
invention, it is preferable to use less than 90% filler by weight
in a polymer/filler mixture or suspension. In embodiments, the
amount of filler, if any, is selected depending on the desired
viscosity of the alpha particle barrier layer so as to enable full
or partial gap filling between the substrate and device and/or
retention of the layer between the substrate and die during
operational temperatures.
[0022] Optionally, a solvent may be added to the neat polymer or
polymer/filler mixture or suspension as a temporary carrier to
lower the viscosity of the barrier material and aid in application
to the substrate-device gap. Any solvent is suitable provided that
the solvent does not substantially deleteriously affect the alpha
blocking or dielectric properties of the barrier during use and it
is safe for handling and disposal. After application of the
reworkable alpha particle barrier the solvent can be removed by
evaporation at room temperature or by heating at elevated
temperatures, or by any other conventional method. Examples of
viscosity-lowering solvents include one or more organic solvents
selected from the group of paraffins (such as heptane, octane),
alcohols (ethyl, isopropyl), ethers, esters, amides, lactones,
ketones, and aromatic hydrocarbons. Some typical examples include
N-methyl-pyrrolidone (NMP), diglyme, triglyme, xylene, amyl
acetate, and acetophenone.
[0023] The polymer and optional fillers are selected so as to
withstand package 2.sup.nd level attach to a printed circuit
board/card and operational temperatures, yet still allow chip
rework using conventional cleaning tools and methods. Chip rework
when using a neat or filled polymer as the reworkable alpha
particle barrier can be performed, for example, by washing with,
for example, xylene, rinsing with a cleaning solvent such as
isopropanol (IPA), and then drying with nitrogen. Additional
suitable cleaning solvents include polar and non-polar fluids,
protic and aprotic fluids, including N-methylpyrolidone, acetone,
common aldehydes, ketones, tetrahydrofuran, HFIP and
gamma-butyrolactone. It should be noted that any conventional
cleaning tool, cleaning solvent, or method can be used to perform
device reworking of the second embodiment of the present
invention.
[0024] The physical state of easily reworkable alpha particle
barrier material of a second embodiment of the invention is ideally
in the B-stage, that is, in an intermediate stage in the
polymerization process and not completely cured. Such a state
allows easy reworking of the die with only conventional cleaning
techniques, and optionally heating. However, presence of the
material in the B-stage is not required. Alternatively, the easily
reworkable alpha particle barrier material can be a polymer or
filled polymer. The invention contemplates the reworkable alpha
particle barrier material to be in any stage, provided that it is
easily reworked with only conventional cleaning techniques, and
optionally heating.
[0025] Generally, the reworkable alpha particle barrier material is
manually, or with an auto-dispense tool, dispensed on at least on
side of a gap-between the chip and substrate to partially or fully
fill the C4 cage. Optionally, the substrate, or the material, or
both may be treated to reduce the viscosity and aid the flow of the
alpha particle blocking material, such as by way of heating, low
frequency vibration, ultrasonic vibration, or combinations thereof.
Techniques such as heating facilitate the flow of the material into
the area between the substrate and the device (C4 cage). Ideally,
the material is drawn into the C4 cage by capillary action, and the
material is expected to remain in the C4 cage by way of surface
tension.
[0026] Additionally, containment methods to retain the reworkable
alpha particle barrier material in the gap between the chip and
substrate can also be included. For example, o-rings or meshes may
be used to minimize flow out from under the die region and/or to
provide dam formation to retain thickness of the material and
provide containment for adjacent component isolation. The barrier
material is at least substantially contained in the gap between the
surface of the chip and the surface of the substrate, for example,
after application at least a portion of the material remains
between both the chip and the substrate, although simultaneous
contact with both the chip and substrate are not required.
EXAMPLE 1
[0027] A PAO oil alpha blocking material (SpectraSyn.RTM. Ultra
300) with a viscosity of about 300 cSt (at 100.degree. C.) was
dispensed with a syringe around the perimeter of chip(s) connected
by C4 connections to a substrate. Capillary action drew the
material under the chip and around the C4 connections, wherein the
spacing between the die BLM (bond limiting metallurgy) and
substrate TSM (top surface metallurgy) are between about 70 and 100
.mu.m.
[0028] The chip(s) were then tested to ensure proper connection to
the substrate. The chip(s) can easily be removed if faulty
connections are found by washing the dispensed area with xylene,
rinsing with isopropanol and then drying with nitrogen. Although
not required, the chip and substrate and/or the oil can be heated
to 60-85.degree. C. to lower the material viscosity and facilitate
the flow of the material into the C4 cage. The alpha barrier
effectiveness of the oil was demonstrated by first measuring the
alpha particle count off an MCM ceramic surface and comparing it to
the count from the same substrate surface coated with a thin layer
of oil as shown in table below. TABLE-US-00001 Alpha Counts
(background Sample subtracted)/Cm.sup.2/Kh Baseline (Ceramic
Substrate 1) 63.8 .+-. 7.8 Substrate 1 coated with PAO-100 oil 2.1
.+-. 5.2 Baseline (Ceramic substrate 2) 49 .+-. 7.9 Substrate 2
coated with 4.3 .+-. 5.4 PAO-150 (SpectraSyn .RTM. 150) oil PAO
oils on Si wafer: SpectraSyn .RTM. 150 3.4 .+-. 2.3 SpectraSyn
.RTM. 300 2.8 .+-. 3.5 SpectraSyn .RTM. 1000 4.8 .+-. 5.5
EXAMPLE 2
[0029] A low molecular weight thermoplastic polymer alpha blocking
material polyisobutylene, was dispensed with a syringe around the
perimeter of chip(s) connected by C4 connections to a substrate.
The chip-joined substrate and the polymer were heated to about
85.degree. C. to lower the viscosity of the polymer and improve its
flow. Capillary action drew the material under the chip and around
the C4 connections, wherein the spacing between the die BLM (bond
limiting metallurgy) and substrate TSM (top surface metallurgy) are
between about 70 and 100 .mu.m.
[0030] The chip(s) were then tested to ensure proper connection to
the substrate. The chip(s) can easily be removed if faulty
connections are found by washing the dispensed area with xylene,
rinsing with isopropanol and then drying with nitrogen.
[0031] While the invention has been described with reference to
exemplary embodiments, it is understood that the words, which have
been used herein, are words of description and illustration, rather
than words of limitation. Changes may be made, within the purview
of the appended claims, without departing from the scope and spirit
of the present invention in its aspects. Thus, although the
invention has been described herein with reference to particular
materials and embodiments, the invention is not intended to be
limited to the particulars disclosed herein; rather, the invention
extends to all functionally equivalent structures, methods and
uses, such as are within the scope of the appended claims.
* * * * *